A multitude of data transmission systems currently called “last mile” or “last foot” are designed to provide high-capacity data access service directly to and from end-user premises. A number of these data transmission systems use RF transmissions. Some of these systems, called “point-to-point”, exclusively connect a single end-user to a service provider, the Internet backbone or the like. Others of these systems, called “point-to-multipoint”, are shared by a number of end-users for such a connection.
A fundamental characteristic of many existing systems, both point-to-point and point-to-multipoint, is that their RF transmissions are protected and regulated by a government body. A fundamental problem with protected, regulated RF transmission systems is that only a few such systems can operate in any given geographic area due to the limited RF frequency spectrum allocated to data access services.
Other unprotected but regulated RF frequency spectrums are allocated to data access services or to multiple shared services. When a high-capacity data access service provider is unable to provide service in a given geographic area because protected, regulated RF frequency spectrum is unavailable, it is desirable to use unprotected, regulated RF bands to be able to provide high-capacity data access service.
The Federal Communications Commission created one such unprotected, regulated RF frequency spectrum allocation in 1997. The Unlicensed National Information Infrastructure (U-NII) includes three frequency ranges of 5.15-5.25 GHz, 5.25-5.35 GHz and 5.725-5.825 GHz in which a multitude of data access service providers and others may operate systems in an unprotected, competitive fashion across the United States. The U-NII frequency spectrum is regulated according to FCC Rules, Part 15.
Since creation of the U-NII a number of standards for equipment operating in the U-NII frequency spectrum allocation have been defined and equipment has been built which uses the U-N11 frequency spectrum allocation. One standard, by the IEEE standards group, designated IEEE 802.11a, specifies the operational parameters of equipment and systems using the 5.15-5.25 GHz and 5.25-5.35 GHz U-NII spectrum allocations for RF transmissions of high-capacity data access service. A standard by the European ETSI BRAN has defined the operation of equipment and systems in the U-NII spectrum.
Interference between the multiplicity of RF transmissions using the U-NII spectrum allocations at the same time in a given geographic area causes degradation in the quality of high-capacity data access in that area. Many techniques can be used to mitigate the degradation and restore the quality of the high-capacity data access to some degree. For example, the aforementioned standards employ interference mitigation techniques.
Well known techniques variously called, error correction encoding or forward error correction (FEC) reduce the information passing through a data transmission system to a point somewhere below the maximum information-carrying capacity of the data transmission system for error-free corrected data transmission in the presence of interference.
For FEC in a prior art point-to-point system, the information content need only be reduced for two connections, to and from the single end-user. In a point-to-multipoint system each end-user in the system has two connections to be considered. The downstream connections to the end-users come from shared central equipment. When the information content reduction of the downstream signal does not vary from user to user and too little information content reduction is performed, the number of end-users who can establish a useable connection will be reduced. However, if too much information content reduction is performed, the data rate for end-users who require little information content reduction will be slower than optimal, and the average data rate of the downstream signals will be reduced below optimal. Therefore, it is desirable to provide the highest error-free downstream data transmission capacity and the maximum subscriber coverage by varying information content reduction for each end-user in an RF wireless data transmission system.
Typical prior art high-capacity data access systems using RF transmissions in the unprotected, regulated frequency bands might provide multiple downstream connections, to the same location, each with a different fixed interference mitigation technique. An end-user connects to the highest-rate downstream it can reliably use. As long as the requirements for each end-user are within the capacity of the selected downstream this approach allows the maximum number of subscribers to be connected. However, each subscriber is forced to use only the limited capacity available through the available bandwidth slices.
Alternatively, a prior art high-capacity data access provider using RF transmissions in the unprotected, regulated frequency bands might provide a single downstream connection with interruptions in the downstream signal during which drastic changes of the downstream FEC parameters and modulation occur. These interruptions cause unusable time during which messages cannot be sent, but higher efficiency of transmission results during all other times.
Also, in point-to-multipoint systems using unprotected, regulated RF spectrum it is likely that interference will vary greatly and suddenly over time. Hence, an interference mitigation system which results in end-user coverage normally considered adequate may suddenly result in reduced end-user coverage.
Therefore, it is desirable to provide a downstream RF transmission technique for high-capacity data access, which will provide varying information content reduction on an end-user-by-end-user basis. Such a desirable system will allow connection by the maximum number of end-users and will not cause reduction of the capacity available to an end-user by making parts of the spectrum unavailable to that end-user. The desirable system will allow any single end-user to use as much of the available spectrum as the capacity of his information content reduction allows during a time that he is scheduled to receive data. Such a desired system should allow equipment at the end-user premises to operate in a superior fashion with respect to interference mitigation when compared to prior art wireless RF data transmission systems operating in the unprotected, regulated frequency bands. Also, such a system should minimize the loss of service availability during interference events.